The technical field of the present invention applies to hydrocarbon-carrying sea pipes and in particular to pipes being periodically bent.
For water depths of several hundred meters, the pipe material is selected from those allowing flexible pipes which well withstand the dynamic loads resulting from ocean swells and currents at the oil extraction site. However, at lower depths, this design is more expensive on account of the unit-length cost of flexible pipe.
The exhaustion of the offshore hydrocarbon reserves of conventional operation has led to searches at great depths (of the order of a kilometer). In this case oil conveyance very often is assured by steel pipes used at every stage of extraction and in particular by vertical pipes between the bottom and the sea""s surface: in English such pipes are called xe2x80x9crisersxe2x80x9d. The conventional architecture of such a complex is a floating platform into which issue the risers of which the dynamic portion has a length from several hundred meters to a few km. Technically and economically these pipes must not be connected to a rigid structure and must be dimensioned to withstand repetitive loads of large amplitudes. In this geometry and in practice, the steel conduit is considered flexible and therefore is able to withstand dynamic loads at a lesser cost. However this technology is degraded by the short fatigue life of the pipe welds: This conduit is constituted of intermediate pipes about 12 m long each and for instance joined end to end by circumferential welds.
The life of a circumferential weld depends mainly on its quality and on the periodic and dynamic loads it is subjected to.
It is known that the fatigue life of the steel constituting the pipes of a conduit is much higher than that of the welds: the welds are susceptible to micro-cracks and then potentially may rupture.
Accordingly it is the objective of the present invention to create local reinforcements for the welded pipes to increase their rigidity and decrease their shapes. Therefore the pipe conduit""s flexibility will be provided by its weld-free portions which are much more fatigue-resistant.
Thus the invention relates to a device reinforcing a circumferential weld of two contiguous pipes which are part of a conduit which shall convey hydrocarbons at sea and comprising a rigidifying element firmly joined by a connection means to said pipes, said rigidifying element being slipped over the two pipes substantially opposite the weld, said reinforcing device being characterized in that the connection means is a mechanical one and is implemented by part or all of the rigidifying element being shaped directly onto the two pipes.
In one feature of the invention, said shape is implemented substantially near the ends and median portion of the rigidifying element.
In another feature of the invention, an elastoplastic material is inserted prior to shaping between the rigidifying element and the pipes either in localized or in continuous manner to limit point stresses on the pipes.
In still another feature of the invention, the inserted material consists of polypropylene or polyethylene or soft steel.
In yet another feature of the invention, the rigidifying element is a hollow element, or a sleeve.
In one embodiment variation of the invention, the invention also relates to a rigidifying device for a two-pipe circumferential weld which comprises a rigidifying element firmly joined by a connection means to said pipes, where said rigidifying element is slipped over the two pipes substantially above each weld, and said reinforcing device is characterized in that the connection means consists of a filler inserted into the play between the pipes and said rigidifying element in order to reduce the stresses arising from the periodic bending of the conduit.
Advantageously the reinforcing element consists of a bush preferably of the same material as the pipes"".
Advantageously again, the filler is a hardening material such as resin or cement.
Advantageously again, the filler is kept in place by shaping the ends of the bush.
The invention offers the foremost advantage of improving the pipe""s fatigue life at the weld site.
Another advantage of the device of the invention is a significant drop in the danger of rupture and hence danger of production losses.
Another advantage is the increase in service life of the conduits and hence lowering production costs.
Lastly the invention provides a simple and economic design.